How to make distilled water from RO water?

December 3, 2025 •

4 min read

While reverse osmosis (RO) water is already highly pure, containing 90-99% fewer contaminants than tap water, a second distillation step can remove nearly 100% of all dissolved solids. This process is ideal for applications demanding the highest level of water purity, such as medical equipment or laboratory work.

Quick Summary

This article outlines a straightforward, step-by-step method for home distillation using reverse osmosis water. It details the simple equipment needed, the thermal process of evaporation and condensation, and the specific applications where this level of purity is beneficial.

Key Points

Start with RO: Use reverse osmosis water as a cleaner source to begin the distillation process, making the end product purer.
Equipment: All you need are a large pot, a heat-safe bowl, an inverted lid, and ice.
Boil and Condense: Heat the RO water to boiling, and use the chilled lid to condense the rising steam into pure water droplets.
Higher Purity: Distilling RO water removes any residual impurities or volatile chemicals that might pass through the RO membrane.
Ideal for Special Uses: The resulting high-purity water is best for applications where mineral buildup is undesirable, such as in CPAP machines, irons, and laboratories.
Storage is Key: Always store the finished distilled water in a clean, airtight glass container to prevent recontamination.

Why Distill Already-Purified RO Water?

Reverse osmosis (RO) systems use pressure to force water through a semi-permeable membrane, effectively filtering out most dissolved salts, chemicals, and heavy metals. However, a standard RO system may not eliminate 100% of contaminants, particularly volatile organic compounds (VOCs) that can pass through the membrane. Distillation, by contrast, removes virtually all impurities by separating water molecules from heavier substances through boiling and re-condensation. Combining these two methods—using RO water as the source for distillation—allows for the production of extremely high-purity water, providing an extra layer of confidence for sensitive applications. This double purification process ensures that even trace minerals or chemicals that might have bypassed the RO membrane are eliminated, resulting in a product that is cleaner than either method alone can achieve.

The Home Distillation Method: Step-by-Step

This method requires only basic kitchen items and is a simple, low-cost way to make distilled water. Always use safety precautions when working with boiling water and hot items.

Equipment Needed

A large stainless steel pot with a lid that can be inverted.
A heat-resistant glass bowl that can be placed inside the pot and floats or is elevated above the bottom.
A cooling agent, such as ice cubes or a cold pack.

The Distillation Process

Prepare the Setup: Fill the large pot halfway with your RO water. Place the glass bowl inside the pot so it sits in the water but does not touch the bottom directly. The water level should not be high enough to enter the bowl.
Boil the Water: Bring the RO water to a rolling boil over medium-high heat. As the water boils, it will evaporate and turn into steam, leaving behind any residual minerals and impurities in the pot.
Condense the Steam: Invert the pot's lid and place it upside down on top of the pot. Immediately place a tray of ice cubes on the inverted lid. The cold surface will cause the rising steam to condense back into liquid water droplets.
Collect the Distillate: The condensed, now-distilled water will drip from the center of the inverted lid into the glass bowl positioned below. Continue boiling and collecting until you have the desired amount of distilled water.
Finish the Process: Once you are finished, turn off the heat and allow the entire setup to cool down completely before handling. Carefully remove the lid and retrieve the bowl containing your fresh distilled water. Store the water in a clean, airtight glass container.

RO Water vs. Distilled Water

While both methods produce clean water, their effectiveness and applications differ. Here is a comparison to help you understand the nuances.


Factor	Reverse Osmosis (RO) Water	Distilled Water (from RO water)
Principle	Water is forced through a semi-permeable membrane under pressure.	Water is boiled, evaporated, and then condensed back into a liquid.
Purity Level	Removes up to 99% of contaminants, but can miss some volatile compounds.	Nearly 100% pure; removes almost all dissolved solids and VOCs.
Energy Use	Less energy-intensive than distillation, relying on water pressure.	High energy consumption is required to boil the water.
Speed	Generally faster than home distillation for producing a quantity of water.	A slower process, dependent on boiling and condensation time.
Water Yield	Produces wastewater (brine) alongside purified water.	No brine produced; all leftover impurities remain in the boiling pot.
Contaminants	Effective against salts, heavy metals, and large particles.	Kills microorganisms and effectively removes most contaminants.
Taste	Often retains some minerals, resulting in a fresher taste.	Flat or bland taste due to the removal of all minerals.

Common Uses for Double-Purified Water

Using distilled RO water ensures the highest possible purity, making it suitable for applications where any mineral or chemical residue could cause problems.

CPAP Machines: Prevents mineral buildup in the humidifier, which can breed bacteria and shorten the device's lifespan.
Steam Irons and Garment Steamers: Eliminates hard water stains and scaling in the appliance's heating element.
Car Cooling Systems and Batteries: Essential for preventing corrosion and mineral buildup in lead-acid batteries.
Aquariums: Provides a neutral base for fish tanks, allowing for precise control of water parameters by adding specific minerals.
Laboratory and Medical Use: Critical for cleaning lab equipment and for applications like sterilizing medical tools.
Cosmetics and Skincare: Ensures the purity of products by using toxin-free water as a base.

Conclusion

While RO water provides a high level of purification for everyday consumption, distilling it offers a pathway to achieve near-total purity for specialized tasks. The simple process of boiling and re-condensing RO water effectively removes any remaining volatile compounds and microorganisms, making the final product ideal for sensitive appliances, lab work, and medical equipment. By using this cost-effective, at-home method, you can produce the purest water necessary for your specific needs.

For more information on water treatment methods, you can consult resources like the Purdue University Extension on Distillation.

Frequently Asked Questions

Distilling RO water is not necessary for drinking, but it helps achieve a higher level of purity for specific applications. It removes any trace volatile organic compounds (VOCs) that might have bypassed the RO membrane, creating water that is virtually 100% pure.

Yes, it is safe to drink. However, due to the removal of all minerals and dissolved gases, many people find that distilled water has a flat or bland taste. The minerals we need for health are primarily obtained from a balanced diet, not water.

RO water often has a fresher taste because it can retain some beneficial minerals. Distilled water has a flat, neutral taste because the distillation process removes all dissolved solids, leaving only pure H₂O.

No, distillation is an energy-intensive process as it requires boiling water. For general consumption, a standard RO system is far more energy-efficient.

For best results, use a large, stainless steel pot and a heat-resistant glass bowl. Avoid using aluminum, as it may leach into the water during boiling.

The duration depends on the volume of water you are distilling. A batch of 1-2 gallons can take an hour or more, including the time to boil and condense the water.

Yes, you can distill tap water. However, starting with RO water will result in a much cleaner final product and leave less mineral residue (scaling) in your pot to clean afterward.